While world-wide demand for various types of fish and other marine food products has been steadily increasing, both as a result of population increases and because of an increasing world-wide taste for fish-based protein over red meat, the worlds fishery resources are becoming increasingly depleted as a result of over fishing and various environmental problems. Efforts have heretofore been made to overcome the depleted fish resources by use of fish farms; however current fish farming techniques, which include flow through/pump to shore facilities, ponds and marine net pens, face a number of environmental and production constraints which limit their flexibility, expansion potential and economic viability.
First, most of these facilities have very high water consumption, sometimes requiring roughly 10,000 gallons of water to produce a single pound of fish. This requirement for huge quantities of water at substantially constant temperature imposes severe environmental restrictions on placement and operation of aqua-farms, particularly those utilizing the flow-through and pond techniques.
There are also chronic production risks and loses in such a venture which arise as a result of various factors including pollution, uncontrolled transmission of disease, algal blooms and storm damage. Concern also exists over the risk of genetic contamination and disease transmission to wild stocks by escaped farm fish as well as pollution to ocean and waterways resulting from the nutrient loading resulting from the operation of aquaculture facilities.
A declining return on biomass is another problem, it taking an average of two pounds of fish meal-based feed to produce one pound of shrimp or salmon. Similar problems exist for other species.
Production costs are also very high for fish farms because of the substantial land and water area required for the farms, and the fact that such land must be adjacent to a significant water resource, making the land prime land for other uses and therefore relatively expensive. Market limitations also arise due to intermittent product availability which is dictated by factors including climate and seasonal fluctuations, the difficulty of controlling quality of the end product and of protecting from losses as a result of various environmental factors, and the lack of product diversity, since such farms can generally only produce indigenous species.
A need therefore exists for an improved technique for performing fish farming which dramatically reduces water usage, has little or no environmental impact on the surrounding area, protects the seafood stock being grown from disease, pollution, and other potential environmental problems, provides a controlled environment so that product availability and product diversity are independent of the local environment, does not require large land utilization and/or can be located in a relatively inexpensive locations and provides enhanced return on biomass by more efficient use thereof. The ability to collect and utilize waste such as manure and uneaten food and to profitably recycle such waste is also desirable.
A system offered by AquaFuture, Inc., the assignee of this application, overcomes many of the above problems by permitting the fish or other seafood (sometimes collectively referred to hereinafter as "fish" or "seafood") to grow within a controlled environment, for example a large tank, through which water is flowed at a selected rate, with most of the water leaving the rearing environment/tank being purified by for example filtration and degassing, and being aerated before being returned to the tank. The water may also be disinfected during the processing of the water before being returned to the tank. This system is advantageous over the prior art fish farms in that it uses 5% to 10% or less of the water required by other fish farms, thus making it possible to locate the fish farm in areas with modest water resources and significantly reducing water costs for the system. Further, since the water is purified, and if necessary disinfected, before being applied to the tank, and the temperature of the water can also be controlled during the processing, the quality of the available water supply is not critical. Further, since the system is substantially a closed loop system and is self-contained, the system does not pose a contamination risk to wild stock, nor is there a danger of disease or contamination of seafood being grown from wild stock. The ability to operate in a completely controlled environment reduces production risks and losses as a result of factors such as pollution, disease and storm damage, and also removes some of the market limitations resulting from climate and seasonal fluctuations, permitting greater product diversity and substantially year-round operation. The controlled environment also facilitates quality control and permits more efficient utilization of feed, both of which result in improved profitability.
However, existing water reuse technologies generally segment the various water treatment processes into distinct stages, with each stage generally requiring a separate vessel as well as piping connections, control valves, etc. Since these systems typically circulate very large volumes of water, it is critically important that the treatment process be as efficient as possible. Additionally, the sequence of the various unit processes is a significant factor in determining the process efficiency as well as the quantity of feed which can be applied to the system and to the resulting water quality. Reducing the equipment capital cost and increasing process efficiently are critical determinants of success for these systems.
Another problem in these systems is to efficiently remove dead and moribund fish from the tank and to efficiently remove excess feed and manure or other droppings from the livestock. Since it is possible that dead or moribund fish may be diseased and there is a possibility that these fish will spread disease either by water-borne transmission or by being cannibalized by other fish in the tank if they are left in the tank for any period of time, it is important that the dead and moribund fish be removed from the tank relatively quickly and that cannibalizing of these fish while they remain in the tank be minimized. Cannibalization also makes it more difficult to determine inventory losses and thus hinders inventory management. Further, in systems with multiple tanks, nets and divers for removal of dead fish would normally move between tanks, enhancing the possibility of disease spreading within the system. Removal of excess food and of manure is also important to maintain water purity and tracking excess feed can facilitate more efficient feed management. It is important that both the removal of the dead and moribund fish and the removal of excess feed and manure be accomplished in a manner so as to minimize water loss from the closed system, thereby reducing the amount of make up water which must be supplied to the system.